ASTRONOMERS DISCOVER UNUSUAL STAR SYSTEM WITH POSSIBLE BLACK HOLE

COLUMBUS, Ohio -- An Ohio State University astronomer is part of a team that
has identified a new and unusual binary star system in our galaxy. The
system includes a normal star paired with a dark and massive object such as
a neutron star or black hole that is ejecting two high-speed jets of
material.

The massive object's companion, the star CI Camelopardalis (CI Cam for
short), isn't new to astronomers -- it was first spotted in 1933 when
observers noted the peculiar wavelengths of light it emitted. But when a
NASA satellite picked up an intense burst of X-rays from the star early last
week, CI Cam thrust itself into the center of an astronomical debate about
how binary star systems evolve.

R. Mark Wagner, an Ohio State astronomy research scientist in
residence at Lowell Observatory in Flagstaff, Az., knew something
extraordinary was happening when he received the coordinates of the X-ray
outburst from NASA Goddard Space Flight Center, and then, very soon
afterward, received coordinates for a radio outburst in the same area. The
radio signals were recorded by the Very Large Array (VLA) radio telescope at
the National Radio Astronomy Observatory in Socorro, New Mexico.

"Only a handful of stars are known radio sources," said Wagner, "and they
usually turn out to be part of exotic binary systems that contain neutron
star or black hole companions."

Wagner found that the coordinates of the radio signals matched the location
of CI Cam. He and Sumner G. Starrfield, a professor of physics and astronomy
at Arizona State University, quickly recorded its spectrum with the Perkins
72-inch telescope at Lowell.

Each chemical element has its own unique spectrum, and Wagner noticed the
presence of large quantities of iron -- a characteristic that made CI Cam
unusual 65 years ago. But this time the spectrum also indicated the presence
of ionized helium -- a sure sign that CI Cam was part of an unusual binary
system that had just undergone a cataclysmic event. The star also appeared
about 10 times brighter than normal.

"That was it," said Wagner. "We had an X-ray source, a radio source, and a
bright object with the optical signatures of an X-ray source all tied
together, so there was no doubt that CI Cam was the optical and radio
counterpart of the original X-ray source."

Wagner said that CI Cam fits the description of an X-ray nova, a binary star
system consisting of a normal star and a massive companion object such as a
neutron star or black hole which undergoes large X-ray eruptions. Decades
can elapse between such events.

"What is obvious now is that CI Cam is a binary system," said Wagner.
"There's not just one star, but two objects -- one of which is either a
neutron star or a black hole. We don't know yet which one. But CI Cam is
very different from many other binaries we know that have neutron stars or
black holes."

That is in part because CI Cam's X-ray burst peaked 10 hours after it began,
and then faded away almost completely over the next two days.

"None of us expected that, because typical X-ray novae have outbursts that
last for about a year, so the brief outburst was an indication that
something is very different about this one. Optically, the star also appears
very different from what we've seen up until this point," said Wagner.

He theorized that CI Cam must be an old, giant star that blasts its
companion with streams of atomic material in a dense wind. The material
coalesces into a disk that orbits the massive companion and slowly spirals
inward under its strong gravitational pull.

The disk may have become unstable at some point, so that all the material
began to fall onto the companion at once. In such a case, whether the
companion is a small, dense neutron star or a black hole, the matter will be
compressed into a very small space -- perhaps less than 50 miles across,
where it is heated to about 10 million degrees and expelled away from the
companion in a burst of X-rays, like those that were observed by the NASA
satellite.

Therein lies some of the current controversy because astronomers
don't agree on what causes the outbursts. Recent observations of
other X-ray novae suggest that an unstable disk is the most likely
explanation, but a brief period of sustained heavy mass loss from the giant
star onto the massive companion could have produced the same result. In
either case, Wagner suggests that the accretion of material from the normal
star onto the neutron star or black hole may have occurred at a
supercritical level, which could have sent material shooting outward from
the north and south poles in the form of two aligned high-speed jets.

The most recent results from astronomers at the VLA corroborate this view,
since they have discovered the presence of high-speed jets of material
emanating from CI Cam. The VLA is also estimating the distance to the star.
Preliminary estimates suggest CI Cam is roughly 3,000 light years from
Earth, well within our galaxy.

Other collaborators in this effort include researchers at the Massachusetts
Institute of Technology, who developed the device on board the NASA
satellite that first received a signal from CI Cam. The device, called the
All Sky Monitor, scans the sky looking for new X-ray sources.

Top -- The location of CI Cam (indicated by the arrow) and the X-ray error
circle as measured by the Proportional Counter Array (PCA) on board the NASA
Rossi X-ray Timing Explorer spacecraft is shown in this visible light
picture of the surrounding region extracted from the Space Telescope Science
Institute Digital Sky Survey. The region shown in the figure covers an area
of the sky comparable to one-quarter the diameter of the full moon.

Bottom -- The location of CI Cam on the sky with respect to prominent
constellations and bright stars is shown. The location of CI Cam is
indicated by an X (just above center and slightly to the left). The chart is
suitable for an observer at 40 degrees north latitude facing northwest at 9
pm EDT on April 15. CI Cam is not visible to the unaided eye but can be seen
using a small telescope.